Non-straight reinforcement fibers in a mortar or concrete based matrix, i.e. bent or deformed fibers, perform satisfactorily because they are not readily pulled out of the hardened matrix. If the fibers interlock with one another and have a curved or bent shape, they are even less prone to be pulled out as the strain in the concrete increases. U.S. Pat. No. 5,443,918 by Banthia et al. entitled "Metal Fiber with Optimized Geometry for Reinforcing Cement-Based Materials" teaches of a metal fiber for reinforcing cement-based materials which comprises an elongated, substantially straight central portion with sinusoid shaped end portions that have a particular engineered designed shape. Other examples of such fibers are taught in U.S. Pat. No. 5,451,471 by Over et al. entitled "Reinforcement Fiber for Reinforcing Concrete" and U.S. Pat. No. 5,162,059 by Rossi entitled "Discontinuous Fiber Made of Drawn Steel Wire, and a Fiber Composite Containing said Fiber." One of the problems involved with the addition of fibers to a concrete composite material includes the difficulty of mixing fiber, especially shaped metal fibers into cementitious material. Fibers that are designed to interlock will tend to tangle or lock together during mixing and form clusters of fibers which are referred to as fiber "balls" such that the fibers never become evenly dispersed throughout the concrete composite material. This phenomenon results in non-uniform fiber composite matrix spaces with no reinforcement fibers yielding a composite lacking in mechanical strength.
This problem is solved by the invention's use of shape memory alloy (SMA) materials that allows the fibers to form complex shapes to assure that it cannot be readily removed from a hardened concrete composite material.